NATURAL OCCURRENCE OF 5 SEED-BORNE COWPEA VIRUSES IN PAKISTAN

A total of 151 cowpea leaf samples with viruslike symptoms were collected from 13 districts of Punjab and North-West Frontier Province (NWFP) of Pakistan during the summers of 1990 and 1991. Desiccated samples were tested by direct antigen coating (DAC) ot double antibody sandwich (DAS) enzyme-linked immunosorbent assay (ELISA) for the presence of seven viruses known to be seedborne in cowpea: blackeye cowpea mosaic (BlCMV) and cowpea aphid-borne mosaic (CABMV) potyviruses, cucumber mosaic (CMV) cucumovirus, cowpea mosaic (CPMV) and cowpea severe mosaic (CSMV) comoviruses, cowpea motile carmovirus (CPMoV), and southern bean mosaic sobemovirus (SBMV). One or more seedborne viruses were detected in 47% (71 of 151) of the symptomatic plant samples. The viruses detected and the percent incidence were: CABMV, 29%; SBMV, 21%; CSMV, 17%; BlCMV, 8%; and CPMoV, 4%. Neither CMV nor CPMV was detected. Seven cowpea seed lots representing two commercial seed types and seven locations in Punjab and NWFP were collected for tests of the same seven seedborne viruses. Only CABMV was seed-transmitted, and only in four of seven seed lots, at frequencies of <1 to 7%. Likewise, although leaf samples collected from plants of a local Punjab cultivar contained four ELISA-detectable seedborne viruses (BlCMV, CABMV, CSMV, and SBMV), only CABMV was transmitted through seeds (7% frequency) from these plants. None of the seven seedborne viruses tested for were detected in 80 of 151 virus-symptomatic samples, suggesting infection with other viruses. This is believed to be the first record of the natural occurrence of BlCMV, CABMV, CPMoV, CSMV, and SBMV in Pakistan and the first report of CPMoV outside of Africa.